Teruo Kurahashi

High-output-power, single-wavelength silicon hybrid laser using precise flip-chip bonding technology

An Si/III-V hybrid laser oscillating at a single wavelength was developed for use in a large-scale Si optical I/O chip. The laser had an InP-based reflective semiconductor optical amplifier (SOA) chip integrated with an Si wavelength-selection-mirror chip in a flip-chip configuration. A low coupling loss of 1.55 dB at the Si-SOA interface was accomplished by both mode-field-matching between Si-SOA waveguides and accurately controlling the bonding position. The fabricated Si hybrid laser exhibited a very low threshold current of 9.4 mA, a high output power of 15.0 mW, and a high wall-plug efficiency of 7.6% at 20 °C. Moreover, the device maintained a high output power of >10 mW up to 60°C due to the high thermal conductance between the SOA chip and Si substrate. The short cavity length of the flip-chip bonded laser expanded the longitudinal mode spacing. This resulted in temperature-stable single longitudinal mode lasing and a low RIN level of <-130 dB/Hz.

A 1 V Peak-to-Peak Driven 10-Gbps Slow-Light Silicon Mach–Zehnder Modulator Using Cascaded Ring Resonators

Slow-light Mach–Zehnder modulators on a silicon-on-insulator substrate are examined in this paper. The phase shifter on each arm consists of ten cascaded ring resonators in an all-pass filter configuration, and this acts as a slow-light structure. Fabricated devices show seven-fold enhancement in modulation efficiency compared with that of a conventional modulator; this enhancement was due to the slow light. Large signal modulations of 10 Gbps have been obtained using a driving signal of only 1 V peak-to-peak.

Compact and low power operation optical switch using silicon-germanium/silicon hetero-structure waveguide

We proposed a silicon-based optical switch with a carrier-plasma-induced phase shifter which employs a silicon-germanium (SiGe) / silicon (Si) hetero-structure in the waveguide core. A type-I hetero-interface formed by SiGe and Si is expected to confine carriers effectively in the SiGe waveguide core. The fabricated Mach-Zehnder optical switch shows a low switching power of only 1.53 mW with a compact phase shifter length of 250 μm. The switching time of the optical switch is less than 4.6 ns for the case of a square waveform driving condition, and 1 ns for the case of a pre-emphasis electric driving condition. These results show that our proposed SiGe/Si waveguide structure holds promise for active devices with compact size and low operation power.

Highly-efficient, low-noise Si hybrid laser using flip-chip bonded SOA

We developed a Si hybrid laser integrating Si wavelength filter and flip-chip bonded SOA. A high-output-power of 14.4 mW and wall-plug efficiency of 6.2% were obtained together with a low RIN level of <;-135 dB/Hz.

Wavelength-tuning-free 10-Gb/s operation of a silicon-integrated resonantly-enhanced modulator and single-mode laser

A modulator with an enhanced efficiency by cascaded microring resonators (MRRs), and a single-mode laser with a wavelength determined by a MRR wavelength filter were integrated on a Si chip to demonstrate for the first time wavelength-tuning-free 10-Gb/s modulation over a wide range of temperature.

Cascaded-ring-resonator-loaded Mach–Zehnder modulator for enhanced modulation efficiency in wide optical bandwidth

A cascaded-ring-resonator-loaded Mach–Zehnder modulator (CRR-MZM) is presented in which a number of cascaded ring resonators (RRs) are loaded in the interferometer as phase modulators. The ability of the design to provide enhanced modulation efficiency at a wide optical bandwidth is demonstrated in comparison with a conventional single-RR-type modulator without an interferometer. The optimization of RRs for the CRR-MZM is investigated experimentally by measuring the transmission spectra in both intensity and group delay of RRs having various structural parameters. Using the optimized parameters, we fabricated a CRR-MZM with 10 cascaded RRs loaded on each arm of the interferometer on a silicon-on-insulate substrate. The RRs had pin-diodes along the waveguides, which were operated with forward bias voltage. Its modulation efficiency was enhanced by a factor of 4.4 at the expense of additional loss of less than 3.5 dB compared with a standard non-resonant MZM. 10 Gb/s-operations of CRR-MZM were successfully demonstrated using pre-emphasized RF signals with amplitude of 1.5 Vpp in a wavelength range of 2 nm.

Hybrid laser with Si ring resonator and SOA for temperature control free operation with ring resonator-based modulator

Si-wire-based hybrid laser consisting of a microring resonator (MRR) and a semiconductor optical amplifier is demonstrated. Novel transmitter scheme potentially makes it possible for a MRR-based modulator to modulate the signal without temperature control.

1-V pp 10-Gb/s operation of slow-light silicon Mach-Zehnder modulator in wavelength range of 1 nm

We developed a slow-light silicon Mach-Zehnder modulator utilizing cascaded ring resonators. It operates at 10 Gb/s with driving voltage of 1 Vpp in a wavelength range of 1 nm without adjustment for the resonant wavelengths.

Characteristics of aluminum substitution technology for self-aligned full metal gate nMOSFETs

We investigated self-aligned metal gate MOSFETs that feature an ideal low-resistance aluminum gate using aluminum substitution technology (AST). This technology can be used to fabricate metal gate MOSFETs with submicrometer gate lengths and 1.8-nm-thick gate insulators processed at 350/spl deg/C. We found that AST is especially suitable for MOSFET with short gate lengths, because the aluminum substitution is accelerated under gate lengths of 0.1-/spl mu/m. We will explain the aluminum substitution phenomenon based on the counter diffusion between aluminum and silicon and the capillary effect. We will also show the electric properties of full metal gate nMOSFET produced using AST with a 60-nm gate length.

Silicon-Wire Waveguide Based External Cavity Laser for Milliwatt-Order Output Power and Temperature Control Free Operation with Silicon Ring Modulator

We report a novel hybrid laser based on a silicon-wire external cavity filter. We characterize the hybrid silicon laser from the viewpoint of high output extraction efficiency and temperature control free operation with a silicon microring resonator. First, it is experimentally verified that output extraction efficiency of the laser is significantly improved by locating an optical coupler within the laser cavity. As a result, we show mW-order output power and wall-plug efficiency of ~0.9%. In addition, we demonstrate that the operating window of the silicon microring modulator is adaptable to the oscillation wavelength of the hybrid silicon laser in regard to temperature change of a silicon substrate from 25 to 55 °C.